Staging: line6: Fix unnecessary space after function pointer in driver.h

This patch fixes the following checkpatch.pl issues in driver.h:
WARNING: unnecessary space after function pointer in driver.h

Signed-off-by: Monam Agarwal <monamagarwal123@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>